1. Field of the Invention
The present invention relates generally to a coating for a transparent substrate. More particularly, the present invention is directed to a multilayered hydrophobic coating for a transparent substrate and method for the manufacture of the same.
2. Description of Related Art
At present, automobile windows and mirrors are typically formed of glass. History has shown numerous disadvantages exist with utilizing glass in automobiles. Glass tends to add a significant amount of weight to automobile, and glass can pose a safety threat to passengers inside the automobile as glass has a tendency to shatter upon breakage. It is highly desirable to provide shatter-resistant glass surfaces in automobiles and other vehicles or to utilize other materials which do not tend to shatter. There are advantages which may be achieved by using highly transparent, optical quality plastic in place of glass. Plastic is lighter, tougher and less likely to fracture than glass. There is a demand for fully practical plastic windows and mirrors in the automotive industry due to its lightweight nature that contributes to the reduction of the gross weight of the vehicle. Further, plastic is advantageous due to its non-breakableness that is favorable to the safety of the driver in case of an accident.
One problem associated with plastic substrates, such as those used in windows and mirrors, is their significantly limited operational service life resulting from warpage or distortion due to the hygroscopic properties of the polymers used in forming the plastic substrate. Unlike its glass counterpart, a plastic substrate formed with a polymer-based material will gradually absorb moisture from the surrounding atmosphere. Over time, the absorption of moisture, coupled with variations in other climatic conditions, causes the polymer-based material to expand and contract. The moisture permeability of various coatings applied to both sides of a plastic substrate will often lead to different amounts of moisture being absorbed by the opposing surfaces of the plastic substrate, thus resulting in uneven expansion and contraction. This can cause a loss in optical clarity through the plastic substrate.
There is a need to provide a coating for a transparent substrate which provides increased durability and weatherability of the transparent substrate while maintaining a desired optical clarity. Furthermore, there is also a need for an improved coating for a transparent substrate which provides added protection against abrasions and impact damage.
The foregoing shortcomings and disadvantages of the prior art are alleviated by the present invention that provides a multi-layer coating which increases the durability and weatherability of a transparent substrate, such as glass, plastic, or other transparent material. The multi-layer coating includes a surface-hardening layer of organo-siloxane formed over the transparent substrate. An abrasion-resistant coating comprising a stack of alternating layers of silicon dioxide and zirconium dioxide is formed over the surface-hardening layer. The multi-layer coating includes a hydrophobic outer layer of perfluoroalkylsilane formed over the abrasion-resistant coating. This multi-layer coating configuration provides a surface for the transparent substrate which resists abrasions and absorbs mechanical stresses while providing an improved weather-resistant barrier for the substrate.